Getter and setter methods in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a getter method in C++?

A getter method is a function that returns the value of a private class member variable. It allows controlled read access to the variable.

beginner

What is a setter method in C++?

A setter method is a function that sets or updates the value of a private class member variable. It allows controlled write access to the variable.

intermediate

Why do we use getter and setter methods instead of making variables public?

Getter and setter methods protect the data by controlling how variables are accessed or changed. This helps keep data safe and allows validation before changing values.

beginner

Show a simple example of a getter and setter for a private int variable named 'age'.

class Person {
private:
    int age;
public:
    int getAge() const { return age; }
    void setAge(int a) { if(a >= 0) age = a; }
};

intermediate

What happens if you try to set a negative age using the setter in the example?

The setter checks if the age is negative. If it is, it does not change the value, so the age stays valid (non-negative).

What is the main purpose of a getter method?

A To read the value of a private variable

B To write a value to a private variable

C To delete a variable

D To create a new variable

A getter method allows reading the value of a private variable safely.

Which keyword usually describes variables accessed by getters and setters?

A static

B public

C private

D const

Variables are usually private to protect them and accessed via getters and setters.

What can a setter method do before changing a variable?

A Validate the new value

B Print the variable

C Delete the variable

D Convert the variable to string

Setters often check if the new value is valid before updating the variable.

Which of these is a correct setter signature for an int variable 'score'?

A void getScore();

B void setScore(int s);

C int getScore(int s);

D int setScore();

Setters usually return void and take the new value as a parameter.

If a class has a private variable, how can code outside the class access it safely?

A Directly accessing the variable

B By copying the class

C Using global variables

D Using getter and setter methods

Getters and setters provide controlled access to private variables.

Explain what getter and setter methods are and why they are useful in C++ classes.

Think about how to safely read and change private variables.

Write a simple C++ class with a private string variable and add getter and setter methods for it.

Remember getters return the variable, setters take a parameter to update it.

Practice

1. What is the main purpose of getter and setter methods in C++ classes?

easy

A. To control access to private variables safely

B. To make variables public automatically

C. To delete variables from the class

D. To print variable values directly

Solution

1. Step 1: Understand encapsulation in classes

   Getter and setter methods are used to access and modify private variables safely without exposing them directly.

2. Step 2: Identify the role of getters and setters

   Getters return the value, setters allow controlled modification, often with validation.

3. Final Answer:

   To control access to private variables safely -> Option A

4. Quick Check:

   Getter and setter = control access [OK]

Hint: Getters and setters protect private data access [OK]

Common Mistakes:

• Thinking getters/setters make variables public
• Confusing setters with printing functions
• Assuming getters modify data

2. Which of the following is the correct syntax for a setter method in C++ to set a private integer variable age?

easy

A. int setAge() { return age; }

B. void setAge(int a) { age = a; }

C. void getAge(int a) { age = a; }

D. int age(int a) { age = a; }

Solution

1. Step 1: Identify setter method signature

   A setter usually returns void and takes a parameter to set the private variable.

2. Step 2: Match correct syntax

   void setAge(int a) { age = a; } matches: void return type, parameter int a, and sets age = a.

3. Final Answer:

   void setAge(int a) { age = a; } -> Option B

4. Quick Check:

   Setter = void + parameter + assign [OK]

Hint: Setter methods return void and take a parameter [OK]

Common Mistakes:

• Using return type int for setter
• Naming setter as getAge
• Setter returning a value

3. What will be the output of the following code?

#include <iostream>
class Person {
private:
  int age;
public:
  void setAge(int a) { if(a >= 0) age = a; else age = 0; }
  int getAge() { return age; }
};

int main() {
  Person p;
  p.setAge(-5);
  std::cout << p.getAge();
  return 0;
}

medium

A. Garbage value

B. -5

C. 0

D. Compilation error

Solution

1. Step 1: Analyze setter behavior with negative input

   The setter checks if the input is >= 0; if not, it sets age to 0.

2. Step 2: Check what happens with -5

   Since -5 < 0, age is set to 0.

3. Final Answer:

   0 -> Option C

4. Quick Check:

   Negative input sets age to 0 [OK]

Hint: Setter validates input before setting value [OK]

Common Mistakes:

• Assuming negative value is stored
• Expecting garbage value from uninitialized variable
• Thinking code won't compile

4. Identify the error in the following setter method and choose the correct fix:

class Box {
private:
  int length;
public:
  void setLength() { length = l; }
};

medium

A. Remove the method entirely

B. Change return type to int

C. Make length public instead

D. Add parameter int l to setLength method

Solution

1. Step 1: Check setter method parameters

   The setter tries to assign 'l' but has no parameter 'l' defined.

2. Step 2: Fix by adding parameter

   Adding 'int l' as a parameter allows passing the value to set length.

3. Final Answer:

   Add parameter int l to setLength method -> Option D

4. Quick Check:

   Setter needs parameter to assign value [OK]

Hint: Setter must have parameter to set value [OK]

Common Mistakes:

• Forgetting to add parameter
• Changing return type unnecessarily
• Making variable public instead of fixing setter

5. You want to create a class Temperature that stores temperature in Celsius but only allows values between -273 and 1000. Which setter method correctly enforces this rule?

hard

A. void setTemp(int t) { if(t >= -273 && t <= 1000) temp = t; else temp = -273; }

B. void setTemp(int t) { temp = t; }

C. int setTemp(int t) { if(t >= -273) temp = t; return temp; }

D. void setTemp() { temp = 0; }

Solution

1. Step 1: Understand the value range requirement

   Temperature must be between -273 and 1000 inclusive.

2. Step 2: Check which setter enforces this range

   void setTemp(int t) { if(t >= -273 && t <= 1000) temp = t; else temp = -273; } checks the range and sets temp accordingly; others do not enforce limits properly.

3. Final Answer:

   void setTemp(int t) { if(t >= -273 && t <= 1000) temp = t; else temp = -273; } -> Option A

4. Quick Check:

   Setter validates range before setting [OK]

Hint: Use if-condition in setter to validate input range [OK]

Common Mistakes:

• Not validating input range
• Setter without parameters
• Setter returning int instead of void